Studies in progress are directed toward uncovering the endocrine and neurocytochemical basis for the exacerbation of the hypertension, with cardiac, blood vessel, and renal morbidity, which is induced by isolation-rearing in mice (Atherosclerosis 14:203, 1971). Investigations of the influence of isolation-rearing upon adrenal cortical function are being completed. In these studies the adrenal cortical response to diverse types of acute and chronic stress are being evaluated in normal and isolation- reared animals. Principal parameters of adrenal cortical function being measured are the thymus involutional response, and the alterations in plasma corticoids. Studies are also being conducted in rats to determine the extent to which the phenomena we have observed in mice also occur in these animals. A newly developed and critical part of our program, which is receiving a highest priority, are studies in monkeys, Sciamiri sciureus. We are attempting to determine if a sustained hypertension, with accompanying morbid heart and kidney changes, may also be induced in these animals by disruption of their social structure and by excess social or emotional stimulation, and if their susceptibility to the development of cardiovascular disease is also increased by isolation-rearing. Studies are also being conducted on the cytochemical bases for the phenomenon of "imprinting" of the defense alarm responses in neurons isolated from CNS controlling centers and of their disruption by isolation-rearing, using the micro-analytical methods of Hyden and Edstrom.